Multimap????? - Codeforces

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Multimap?????

Автор MaxWelll, история, 7 лет назад, По-английски

Can anybody tell me about C++ multimaps. As far as I know you can assign many values to a key but... how do I access to any of theese values?

MaxWelll
7 лет назад
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t3rminated

7 лет назад, # |

map<int,set<int, int> > m;
m[key].insert(values);
m[key].find(x)

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MaxWelll

7 лет назад, # ^ |

← Rev. 3 →

Sorry but I dont get it yet.

I mean for example:

I have 1->2, 2->4, 1->3 and 3->5. That would be as:

key |  values
   1|  {2,3}
   2|  {4}
   3|  {5}

How can I know how many values are assigned to every key and how can I make reference to each of the values a key has?

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DmitriyH

7 лет назад, # ^ |

l = m.lower_bound(key);
u = m.upper_bound(key);
c = std::distance(l, u);

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MaxWelll

7 лет назад, # |

Thanks two of you for help

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yuizy

7 лет назад, # ^ |

Unfortunately they didn't tell you how to use multimap. Here's an example.

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MaxWelll

7 лет назад, # ^ |

That's true, their comments were helpful but what i wanted was an example of using multimap. Could you make a comment with the example, my internet provider does not allow me to go that link

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yuizy

7 лет назад, # ^ |

#include <map>
#include<iostream>
using namespace std;
int main() {
	multimap<int,string> m;
	m.insert({1,"hello"});
	m.insert({1,"world"});
	m.insert({2,"goodbye"});
	m.insert({3,"spacecows"});
	
	cout<<"Number of elements in key 1: "<<m.count(1)<<endl;
	
	auto range = m.equal_range(1);
	for(auto iter = range.first; iter != range.second; iter++) cout<<iter->second<<" ";
	cout<<endl;
	return 0;
}

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MaxWelll

7 лет назад, # ^ |

I see, very ilustrative example. I've never used auto I gess it make the variable get the type that is asigned to it, am I right?

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yuizy

7 лет назад, # ^ |

Yes, the compiler will deduce the type for you. auto is quite a bit shorter to write than pair<multimap<int,string>::iterator,multimap<int,string>::iterator>.

I recommend reading these two posts (C++11 for programming contests... and C++ Tricks) for some additional info on using C++11 in programming contests.

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